HIV-1 Tat Activates Neuronal Ryanodine Receptors with Rapid Induction of the Unfolded Protein Response and Mitochondrial Hyperpolarization

John P Norman,Margarita Trejo,Stephen Dewhurst,Eliezer Masliah,Seth W Perry,Holly M Reynolds,Michelle Kiebala,Harris A Gelbard,David J Volsky,Karen L De Mesy Bentley,Sanjay B Maggirwar

doi:10.1371/journal.pone.0003731

Abstract

Neurologic disease caused by human immunodeficiency virus type 1 (HIV-1) is ultimately refractory to highly active antiretroviral therapy (HAART) because of failure of complete virus eradication in the central nervous system (CNS), and disruption of normal neural signaling events by virally induced chronic neuroinflammation. We have previously reported that HIV-1 Tat can induce mitochondrial hyperpolarization in cortical neurons, thus compromising the ability of the neuron to buffer calcium and sustain energy production for normal synaptic communication. In this report, we demonstrate that Tat induces rapid loss of ER calcium mediated by the ryanodine receptor (RyR), followed by the unfolded protein response (UPR) and pathologic dilatation of the ER in cortical neurons in vitro. RyR antagonism attenuated both Tat-mediated mitochondrial hyperpolarization and UPR induction. Delivery of Tat to murine CNS in vivo also leads to long-lasting pathologic ER dilatation and mitochondrial morphologic abnormalities. Finally, we performed ultrastructural studies that demonstrated mitochondria with abnormal morphology and dilated endoplasmic reticulum (ER) in brain tissue of patients with HIV-1 inflammation and neurodegeneration. Collectively, these data suggest that abnormal RyR signaling mediates the neuronal UPR with failure of mitochondrial energy metabolism, and is a critical locus for the neuropathogenesis of HIV-1 in the CNS.

Highlights

Infection of the central nervous system (CNS) with the human immunodeficiency virus type 1 (HIV) occurs rapidly after primary infection [1]
Due to the importance of the endoplasmic reticulum (ER) in both calcium signaling and mitochondrial function, we investigated the effect of human immunodeficiency virus type 1 (HIV-1) transcription protein (Tat) on sequestration of calcium in the ER and demonstrate that HIV-1 Tat induces the rapid loss in ER calcium through the activation of the ryanodine receptor (RyR) with initiation of the unfolded protein response (UPR)
In our previous studies of cortical neurons exposed to HIV-1 Tat, we concluded that neuronal mitochondria suffered a loss of energy metabolism reflected by decreased NAD(P)H, as well as [Ca+2][39]

Summary

Introduction

Infection of the central nervous system (CNS) with the human immunodeficiency virus type 1 (HIV) occurs rapidly after primary infection [1]. More recent studies of incidence and prevalence of the neurologic component of HIV-1 infection demonstrate that neural injury continues in some patients regardless of the ability of HAART to achieve virologic suppression and normalization of immunologic parameters [3]. The CNS can act as a reservoir for HIV as agents that comprise HAART do not achieve a level of CNS penetration that can fully eradicate the virus [2,4]. In patients with improved systemic health from HAART, it is HAART’s failure to control HIV-1’s effects on the signaling pathways that mediate normal communication between immune effecting glias and vulnerable neurons, that has substantially contributed to the rise in HAND prevalence since 2000 [5]. HAND continues to be a problem of pandemic proportions

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